There is a need for high speed marine vehicles that are beachable to allow discharge of troops and cargo. The Navy's LCU (Landing Craft Utility) has a top speed of about 12 knots is beachable but not amphibious. The Navy has made an attempt in the last few years to update the LCU concept with a new design, dubbed the LCU(R) for LCU(Replacement), to gain more speed. The desire for more speed appears to have been unsuccessful since the design specifications for the LCU(R) have recently been changed to drop the speed requirement from its original 45 knots to a maximum of only 15 knots. This low speed is undoubtedly a problem when one realizes that today's supply ships are required to be at least a hundred miles offshore to help insure their safety from shore based missile attacks. Twelve knots requires a minimum of over eight hours transit time.
An alternative is the LCAC (Landing Craft Air Cushion) that is not only beachable but also amphibious. The LCAC is supported by a blower pressurized air cushion. The LCAC has a full 360 degree peripheral flexible skirt that attaches to the underside of its hull and restrains the air cushion between the hull and a water or land surface. The LCAC and its like are many times referred to as hovercraft. The LCAC has a number of inherent disadvantages, to wit: 1) It does not handle rough seas well, 2) It has an inherent rough “cobblestone” ride due to pressure perturbations in its air cushion where the pressure perturbations are mainly attributed to its full 360 degree flexible seals, 3) It is very weight sensitive, 4) It can only access beachheads that have gently sloped beaches, 4) Its full 360 degree flexible seals are expensive initially and to maintain, 6) Largely due to its need for power from three 4,500 HP gas turbines that supply propulsion and blower power, it is expensive initially with a current price of over $20 million, and 7) It is very noisy due to its necessary air propellers. In spite of these shortcomings the LCAC has been procured in reasonably large numbers due to its very valuable amphibious and 45 knot speed capabilities. The amphibious capability allows driving up onto a beach and discharging troops and cargo on dry land above the surf line.
There is also the recently developed Marine AAAV (Armored Amphibious Assault Vehicle). This is basically a small tank that is designed to also operate in a water environment. It requires a tremendous amount of propulsive power when waterborne since its tank tracks are in water contact at all speeds hence giving the AAAV a very high water drag component. Top speed waterborne is only about 25 knots. Also, due to its rather boxy tank-like shape and heavy weight, it is not capable of operating in heavy seas.
The current Navy/Marine Sea Basing program has pointed out the need for beachable high speed marine transports that are referred to as HSCs (High Speed Connectors). The concept behind Sea Basing is to have large supply ships positioned about 200 miles offshore with troops, supplies, vehicles, etc. transported to beachheads by the HSCs. Some of Applicant's other patent application(s) address this need in the form of large beachable air cushioned marine vehicles. These inventive concepts of Applicant are mostly related to the SeaCoaster® SECAT (Surface Effect CATamaran) high speed marine vehicle.
The instant invention advanced marine vehicle proposed herein offers very high speed at high efficiency and excellent seakeeping as a marine vehicle as well as amphibious capability. It combines high efficiency and high speed air cushioned marine hull technology with retractable land drives. It does this while also offering low initial and maintenance costs. It finds application, as an advanced high speed and very seaworthy vessel that is also amphibious, to a variety of programs. This includes the LCU(R) program, a second generation high speed AAAV type vehicle that is not only amphibious but also an excellent rough sea vessel and would offer waterborne speeds in excess of 50 knots with similar installed power to the 25 knot AAAV, and the Sea Basing program as an amphibious HSC. There are also other applications besides military as commercial and pleasure craft plus heretofore unrealized applications will surface as the technology becomes widely known.